1. Field of the Invention
This invention relates to a picture image communication apparatus and particularly to a picture image communication apparatus capable of communication through a plurality of communication networks having different specifications from each other.
2. Description of the Prior Art
A facsimile apparatus as a picture image communication apparatus is known. Such facsimile apparatus is capable of communication through a plurality of communication networks having different specifications from each other. That is, it communicates through either of the ISDN (integrated services digital network) or a telephone line network. This prior art facsimile apparatus comprises a scanner, a printer, a first interface portion for communication through the ISDN, and a second interface portion for communication through the telephone line network. This prior art facsimile apparatus can effect communication under definitions of CCITT (The International Telegraph and Telephone Consultative Committee) G3 (group 3) through the ISDN network or the telephone line network and G4 (group 4) through the ISDN. Therefore, if communication is effected in G3 mode, the operator of a calling party can select either of networks, namely, ISDN and telephone line network. When the operator selects either of lines, the facsimile apparatus calls using the selected line. If there is no selection of networks, the facsimile apparatus communicate through the ISDN.
The reasons why such prior art facsimile apparatus communicate using the ISDN in G3 mode when the telephone line network is not selected is as follows:
There is another prior facsimile apparatus capable of communication through ISDN via a telephone line network in G3 mode. If this prior art facsimile apparatus communicates with such another facsimile apparatus, the communication fee of ISDN is the same as that in the case that only the telephone line network is used and there are special services, such as a report of fee from the ISDN which is absent in the telephone line network.
However, there is a problem that this prior art facsimile apparatus frequently fails to contact with such another facsimile apparatus in G3 mode using ISDN.
The first reason is an affection of other facsimile apparatus connected to the ISDN line in the bus structure, to which this facsimile apparatus is connected. In the ISDN, if bus line structure is used in the subscriber's line, the maximum of facsimile apparatus connected to one line through the bus line is eight. However, only two channels can be used at the same time. That is, two facsimile apparatus can communicate at the same time. Therefore, if there is no free channel in the bus structure, that is, two facsimile apparatus are communicating, the other facsimile apparatus connected to the bus structure cannot communicate a third party's facsimile apparatus though the third party's facsimile apparatus is ready to communicate.
The second reason is that there is a trouble in the ISDN which is generally rarer than the first mentioned cause.
In consideration of the problems mentioned above, in G3 mode, it is thought of that call is always effected through the telephone line network. However, there is also problem that it is impossible to use the special services of the ISDN. Further, if a trouble occurs in the telephone line network, communication will result in fail totally.
On the other hand, Japanese patent application provisional publication No. 1-284066 discloses a facsimile apparatus which always makes a call with a digital networks in G4 mode when the digital network is available. When the digital network is not available, it makes a call in G3 mode through an analog telephone line network, which may resolve the problem mentioned above. However, in this prior art facsimile apparatus, there is also a problem that the facsimile apparatus selects either of G3 and G4 modes in accordance with only conditions of the networks irrespective of an intention of the operator.